Auto update of program (Downloading from web)

Question

Hello.

I have been creating a application that checks the application version and sees if it fits with the version from http://msbeditor.dumpen.dk/versioninfo.html

If it doesnt I use a webBrowser component to open a download link to http://msbeditor.dumpen.dk/msbEditor.rar

But this is not very practical because, the ones using my application have to download all files even though some of the files are not changed..

So I wanted to ask if you have an idea on how to make a auto updater in C#?

I was thinking of something like:
Check the application version with the online version (Allready done)
If it doesnt fit, then match all the files (last changed or file size or similar) in the rar  file (from msbeditor.dumpen.dk) with the files in the application folder
If they are changed then download the changed files

Any ideas?